294 journal of Comparative Neurology and Psychology. 



are correct, but the intercellular spaces do not occur between the 

 epithelial cells of the plexuses, at least in the forms here studied. 

 Gold preparations show that nerves are present in the plexuses 

 in the vicinity of the large blood vessels. Benedikt (^'J'^ and '74) 

 described nerves in the plexuses of the fourth ventricle, and 

 thought he traced them into the vagus. Findlay ('99) found 

 nerve fibers in the plexuses of man and the calf, by using a modi- 

 fication of Heller's method. These fibers are probably vaso- 

 motor fibers to the blood vessels. 



Fig. 4 shows the cross section of a small irregularity in the 

 plexus of the adult rabbit. In regard to capillaries, connec- 

 tive tissue, and endothelium, it exhibits no particular difference 



from the plexus of the rat. The cyto- 



■^ . ^■- ^%^.- plasm is somewhat more plainly reticular. 



^^ WB-W^ Nucleoli are more evident, and often 



%^{ 'Mj^'^rn'm there is more than one present. Ihe 



#,i);| .^^^*?|V,^ rabbit's plexus is especially character- 



^^•/a\'*^ .'-i^^. .-'^% i^^^^ by the presence of circular or oval 



'?^.is. ^A^--^^'*;.^^ clear spaces. Thev are from 2-6 micra 



~. >...-' indiameter, and really much more numer- 



ous and noticeable than Fig. 4 could in- 

 dicate. The contents are dissolved out 

 by alcohol and xylol. In the ordinary 

 stained sections they show as clear round 

 Fig. 5. Section through an adult or oval areas. The contcnts are of a 

 rabbit's plexus after staining in os- f^^^y natutc, for they readily stain with 



micacid. The protoplasm is faintly • -j CJ TTT T?" ^ ' 



, , , , . ■ osmic acid or budan ill. rig. 'C is a 



granular, and the droplets are stained . ^ i i • 5 i i 



black. Magn,ficat.on X 500. cross section of a rabbit s plexus treated 



with osmic acid. It gives a fair idea of 

 the number of the droplets and their position in the epithelial 

 cells. The basal droplets are the smallest. Toward the apex 

 of the cell, they gradually increase in size. Sometimes one may 

 be seen lying half within, half without the cell. This shows 

 that they are expelled through the top wall. During this 

 process, the nucleus remains entirely unchanged, but rarely it is 

 pressed to one side by the droplet. There is no evidence, how- 

 ever, that the discharge of the droplet is attended by the death 

 of the cell. These fatty droplets have not been found in the nor- 

 mal plexuses of any other form studied. Loeper ('04) speaks 

 of small globules in the plexus of the guinea pig that stain with 



